Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (M. tuberculosis, Mtb), kills more than a million people a year; it is the deadliest infection of humans. Accurate and timely diagnosis of TB is critical for the treatment of patients and prevention of spread of the disease. However, conventional diagnostic tools available to countries with endemic TB suffer from low specificity and low sensitivity. False positivity and false negativity from tuberculin skin test (TST) and sputum smear microscopy have increased the burden in countries where resources are constrained. Definitive diagnosis relies on the growth of TB culture inoculated with sputum obtained from patients suspected of active TB infection. It is a lengthy process normally taking up to two months to reach diagnosis. Modern technology has improved the TB diagnosis in accuracy and decreased the turnaround time, but requires sophisticated equipment and specially trained personnel, which diminishes its practical uses in countries with TB epidemics.
Detection of TB during latent infection is a special problem because during latent infection, Mtb is not present in the sputum. Currently, there is no test to tell if someone is latently infected with TB. Thus, the current skin and blood tests can only tell whether a person has been exposed to TB, but not if they are latently infected.
Accordingly, there is a need to develop a diagnostic tool for active human TB that is accurate, highly sensitive and specific, rapid, cost-effective and simple to use, such that it can be deployed in point-of-care clinics, especially in resource-constrained countries. In addition, there is a clear need for a diagnostic method to determine whether a person is latently infected with TB.